so energy efficiency is really, really important. at the same time what's staying in the house is staying in the house. >> reporter: dr. nathan robinovicz says asthma rate in the u.s. have nearly tripled since 1970, a problem he believes begins at home. the doctor recruited students to carry air monitors several weeks at home and to and from school. after analyzing the quality of the air they were exposed to 24 hours a day, the worst is where you may least expect it. >> the amount of pollution that they were being exposed to was higher inside the home than outside the home for many of the kids. >> reporter: it doesn't surprise hope duncan after her son nearly died from an asthma attack. she learned that dust to mold to pet dander dangers can lurk almost anywhere in our home. >> you never know what's underneath the carpet that you have from pets or from water damage. so there can be things underneath growing that we don't know. >> reporter: changing air filters and cleaning your home often can cut down on breathing problems, but the b